Famicom AV - Microphone Restoration

[Great Hierophant]

One of the few downsides to the Famicom AV, compared to the Famicom, is the lack of a microphone on controller two. It is a really small downside, but there are games that use the microphone (Zelda, Palutena no Kagami) or require it to complete a portion of the game (Takeshi's Challenge).

The microphone, when "used", did two things. First, it mixed the sound with the audio output from the Famicom so you could hear yourself from the TV speakers. Second, it showed up as a button input on $4016 D2. Games can read D2 to determine whether something has been said into the microphone.

Now the Famicom AV condensed three logic chips, the two 40HC368s and the 74LS139, found in the Famicom into a single chip called the Nintendo JIO BU3720S. Its pinout can be found here : http://gammy.void.nu/nesrgb/NES_pio_pinout.txt

As you can see, this chip incorporates only enough logic to support the two controller ports and the expansion port. $4016 D2 is found on neither. However, it could be implemented by adding a 40HC386 and wiring one of its gates it as shown in this schematic : http://nesdev.com/Ntd_8bit.jpg The microphone could also be mixed with the signal from the audio output pins as shown on that schematic, just before the 1μF Capacitor, which I believe is C3 on the Famicom AV.

Of course, there are two practical considerations here. First, you need to find a way to route a wire to a microphone. You could drill a hole in the Famicom AV or perhaps push the wire through one of the vents. The second issue deals with the microphone itself. I do not know the electrical characteristics of the original microphone, and it apparently requires a 4069 Hex Inverter, a capacitor, a volume slider and a resistor to work. It looks like a piezoelectric microphone : http://www.retrofixes.com/2013/10/clean ... ixing.html

[lidnariq]

Given that the BU3270 inside the NES2/Famicom AV connects to CPU D2, you've got a substantially more annoying project here.
You'll either need to completely remove the BU3270, or completely replace how it handles D2.

I'm not certain what the differences are between the BU3266 and the BU3270, if any.

http://vaot.mydns.jp/fc/nfau.htm has some terrifying(ly awesome?) rework.

[Great Hierophant]

Ironically, the front loader NES would be easier to add the microphone, it brings 4016 D2 to the expansion cart connector as well as the signal for audio input to mix the analog microphone with the built-in sound generation.

[Great Hierophant]

From another post on this forum someone linked to a complete set of very nicely computer drawn schematics for the Famicom on this site : http://www43.tok2.com/home/cmpslv/Famic/Famic.htm

There are controller schematics that show how the microphone is wired. All it doesn't do is to give identifying information for the microphone itself.

I could see adding a microphone input to the top loader as well because it has two discrete 40H368s, which give twelve total gates to use. It would be easy enough to determine whether 4016 D2 is already connected to the appropriate chip. If not, one wire would be all it would take to connect the gate and then it would be simple to follow the diagram.

[mikejmoffitt]

From another post on this forum someone linked to a complete set of very nicely computer drawn schematics for the Famicom on this site : http://www43.tok2.com/home/cmpslv/Famic/Famic.htm

There are controller schematics that show how the microphone is wired. All it doesn't do is to give identifying information for the microphone itself.

I could see adding a microphone input to the top loader as well because it has two discrete 40H368s, which give twelve total gates to use. It would be easy enough to determine whether 4016 D2 is already connected to the appropriate chip. If not, one wire would be all it would take to connect the gate and then it would be simple to follow the diagram.

With what software were those schematics made? I see a lot of similar looking ones for the Game Boy from the 1990s.

[wyatt8740]

I have a broken famicom that I can test the mic on, but I'll need to know how I should go about testing it. I know that the circuitry still works, everything but the CPU and one of the RAM chips works.

[mikejmoffitt]

I have a broken famicom that I can test the mic on, but I'll need to know how I should go about testing it. I know that the circuitry still works, everything but the CPU and one of the RAM chips works.

I have a Famicom with a bad PPU that otherwise works. Maybe they can combine powers.

[lidnariq]

What makes an electret microphone? There's not all that much to them to quantify.
For example, here's a datasheet for an arbitrary one I got off Digikey.
Other than geometry, they quantify:

• How much {acoustic power in} produces how much voltage out (sensitivity, measured in Volts/Pascal)
• How much bias voltage is ideal to run (the famicom uses 5V)
• The effective impedance to be balanced against (the famicom uses a 2.2K resistor).
• The frequency response range

So... frequency response and conversion efficiency, the latter can be adjusted for with the volume control on the controller, and the former doesn't vary much (because they're all intended to mostly match human hearing range).

I'd just look on digikey (or your favorite electronics supply store) for something of the correct geometry that takes 2.2KΩ±10% impedance and operates at 5V.

[Great Hierophant]

Here is a source for the BU3270 that is unlikely to go down : http://nesdev.com/nes_pio_pinout.txt

As you can see from the datasheet, the '139 function and the '368 function are physically concentrated in different parts of the chip. The 10K resistor pack is also incorporated into the chip. It would be quite possible to remove the chip and mount a daughterboard with the three chips and resistor pack. With this, you could obtain the extra inverter you need for the microphone and fix the part if it fails. The narrow-DIP package may make it tricky to find a mounting socket.

Everything appears complete and correct except for one thing on the pinout except for one thing: where is the buffered M2 output? You can see M2 go in, necessary for the CPU ROM address decoding, but not come out. M2 is the Clock signal for the shift registers in the controllers, so it is absolutely necessary.

[lidnariq]

The controller's clock signals come directly from the 2A03...

[Great Hierophant]

The controller's clock signals come directly from the 2A03...

Every schematic of the Famicom I have looked buffers the M2 signal with two of the 74HC368's inverters. The NES schematic from Electronix Corp. appears to have an error in its Controller Port diagram where the clock line to the controller is supposed to come from. However, D0-D4 get inverted and buffered on both 368s on the Front Loader NES, but PA13 and the audio signal get their inversion from the 74HC04 on the Front Loader NES and the 368s on the Famicom and NES Top Loader. The BU3270 handles all inversion. Therefore, there are two inverters left on the 368s in the Front Loader NES, what could they be used for?

[lidnariq]

Every schematic of the Famicom I have looked buffers the M2 signal with two of the 74HC368's inverters.

More precisely, it combines M2 with /RD4016 and /RD4017 to produce a signal that's driven low when the famicom is reading from a controller, and floats high the rest of the time. ... because if /RD4016 or /RD4017 is low, M2 is high.

The NES schematic from Electronix Corp. appears to have an error in its Controller Port diagram where the clock line to the controller is supposed to come from.

On my front-loader, /RD4016 and /RD4017 are NOT buffered. They are directly connected to the CPU.

The only mistake on the Electronix corp schematic (on this page, pertaining to this issue) is a missing dot where the signals U8 EN1 and EN2 cross.

Therefore, there are two inverters left on the 368s in the Front Loader NES, what could they be used for?

On my NES-CPU-07, both U7 and U8 connect pin 6 to ground, and pin 7 floats. i.e. completely unused. The other 5 pins (as we knew) buffer D0-D4 from the controller.

[Great Hierophant]

More precisely, it combines M2 with /RD4016 and /RD4017 to produce a signal that's driven low when the famicom is reading from a controller, and floats high the rest of the time. ... because if /RD4016 or /RD4017 is low, M2 is high.

Thank you for that explanation, it helped me understand what the 386's are doing with M2. But if you say that the signal that goes to the controller port is a combination of /RD4016 or /RD4017 and M2, then the BU3270 pinout appears incomplete. All three signals come from the CPU and M2 goes to pin 3, /RD4016 to pin 22 and /RD4017 to pin 23, but where is the combined signal coming from that goes to the controller ports?

[lidnariq]

They already decided for the US front-loader that that was unnecessary. I wouldn't be the least bit surprised if for both the Famicom AV and the US top-loader they just connect the CPU /RD4016 and /RD4017 signals directly to the ports, without being buffered.

[Great Hierophant]

They already decided for the US front-loader that that was unnecessary. I wouldn't be the least bit surprised if for both the Famicom AV and the US top-loader they just connect the CPU /RD4016 and /RD4017 signals directly to the ports, without being buffered.

If I had a multimeter or continuity tester, I could tell you about the Famicom AV, but all I have is an LED-based circuit tester Now I understand, /RD4016 and /RD4017 (aka /INP0 and /INP1) are each connected to a 386 and its respective controller port pin on a Front Loading NES and act as the clock source for the 4021 shift register in the NES controllers.